1. Field of the Invention
The invention relates to an apparatus for safely lowering a person from an elevated position, such as a high-rise building.
2. Discussion of the Prior Art
A serious need has existed for many years for an apparatus which permits a person to be safely lowered from a substantial height. This need has become increasingly acute as the height of buildings has come to exceed the maximum reach of extension ladders. The only safe means now commonly used for removing people from the upper floors of modern high-rise buildings is with the use of helicopters, which is slow, difficult, expensive and is often impossible due to the lack of sufficient landing space on the roofs of such buildings.
Various designs have been developed over the years which might have some applicability to lowering a person from a substantial height. One such prior art apparatus is marketed under the designation "Rescumatic" and includes a toothed pulley with a coaxially mounted braking system including a pair of radially offset brake shoes with radially inwardly articulated flyweights disposed therebetween. As the rate of rotation of the pulley increases (resulting from an increase in the rate of descent of a person holding on to one end of the rope), the flyweights tend to be displaced outwardly, thereby increasing the force of the brake shoes against a stationary brake drum to provide additional braking. However, because the Rescumatic is only a pulley, there is always a downwardly extending free end of rope which is susceptible to becoming hung up, causing the descending person to jerk to an abrupt stop. This would obviously present a serious danger. Moreover, the free end is going to be subjected to heat if the apparatus is being used during a fire, thereby preventing the possibility of resulting degradation of the rope. This degradation is a serious drawback because it could cause slippage through or tearing by the pulley teeth, presenting further possibility of catastrophic failure of the apparatus.
Another prior art apparatus is disclosed in U.S. Pat. No. 3,602,483 to Russell et al. This patent discloses a reel-type apparatus utilizing a metal ribbon which is unwound as the device lowers the person to the ground. The device has a reel section and a coaxial brake section. The brake section includes four pivotally and rotationally mounted brake shoes which are exerted outwardly against a stationary brake drum by leaf springs. When the reel is rotated and the ribbon is let out, the pivotal action of the brake shoes increases braking as the rate of rotation of the reel increases. This increase in braking is intended to slow the reel speed to maintain descent at a relatively slow, regular rate.
While the Russell apparatus appears to have some advantages, there are several serious drawbacks. First Russell's apparatus travels downwardly which the person as he is being lowered. The two primary disadvantages which such construction are (1) that it necessarily adds to the weight which is traveling downwardly, thereby increasing the downward momentum, and (2) that it makes rewinding more difficult than if the device is stationarily mounted. Another drawback of Russell's design is that despite the pivotal mounting of the brake shoes, it is unlikely that there would be a substantial increase in brake pressure as the speed of rotation increases, thus making it possible that the rate of descent would increase as the person is being lowered to the ground.
Other patents disclose the desirability of utilizing flyweights to increase brake pressure as the rate of rotation of a reel-type device increases; see, e.g., U.S. Pat. Nos. 1,888,911 to Graffenreid; 1,888,327 to Rosland; 1,593,704 to Morris; 1,308,480 to Caouette; and 425,554 to Stiver et al. Of these patents, Graffenreid is perhaps the most pertinent because it discloses the desirability of incorporating flyweights into a let down apparatus braking system, thereby increasing the proportional variation of the brake pressure as the rate of reel rotation changes. The Stiver et al patent also discloses the desirability of a crank to manually rewind the apparatus for reuse by another person.
Despite the existence of these prior art designs, no one has yet developed an effective system for safely and inexpensively lowering a person from a substantial height.
Hence, it is a primary object of the present invention to provide an improved let down device which effectively and reliably overcomes the aforementioned limitations and drawbacks of the prior art proposals. More specifically, the present invention has as its objects one or more of the following taken individually or in combination:
(1) The provision of an apparatus for lowering persons safely and slowly from a substantial height regardless of the weight of the individual and the height from which the person is being lowered;
(2) The development of a let down apparatus which is simple in construction and therefore inexpensive, and which is compact and therefore portable;
(3) To provide a let down apparatus which includes a manual rewind feature which facilitates relatively fast rewind even by those with minimal physical capabilities;
(4) The provision of a let down apparatus in which the rate of descent slows as the person approaches the ground;
(5) To develop a let down apparatus which permits the user to enter a harness or chair adjacent the apparatus without being lowered until the user is ready;
(6) To provide a let down apparatus which is easily maintained, particularly with respect to the brake portion; and
(7) The development of a let down apparatus in which heat will have little or no effect upon operating characteristics.